1. Field of The Invention
The invention relates generally to integrated circuit attachment to a substrate and more particularly to the electrical and structural attachment of a radio frequency identification RFID chip to a conductive module. More specifically, the invention pertains to a design and method for efficiently attaching RFID chips directly to respective conductive modules.
2. Description of the Prior Art
Radio frequency identification (RFID) systems are known and are useful for remote identification of physical objects. The identifier is also referred to as a “transponder” or “tag.” In most applications, the RFID tag is in the form of an integrated circuit chip that in its barest form is a silicon die sawed from a silicon wafer.
Although RFID systems are proliferating at a rapid rate worldwide, the key to their future success lies in reducing the price of the tag. There are three major factors that drive the cost in manufacturing RFID tags. The first is the chip itself. The second is the final assembly of a module that typically includes testing. Both of these items are being addressed by the manufacturers in a satisfactory fashion. But the third area that drives cost and the one not being advanced is the ability to attach an RFID chip to a module inexpensively.
Presently, there are number of methods used in attaching a die to a substrate. The earliest method is a carryover from standard integrated circuit attachment used in packaging. Referring to prior art FIG. 1, a die 11 is attached onto a substrate 14 with its face up using either an epoxy or eutectic bonding that entails applying heat coupled with scrubbing action. Wire bonding 12 is then used to connect the chip's pads to the substrate's conductive pattern 13. Not only is this assembly method itself costly, but it requires a stiffer and more costly substrate.
A more typical method used by RFID manufacturers today is to place the chip face down against a patterned conductive material, the method commonly referred to as flip-chip bonding (FIG. 2). The bonding pads 22 of the chip 11 are aligned to the conductive pattern 13 to complete the final electrical connection. The ohmic contact formed between the chip and the conductor may take many forms and typically an intermediate conductive epoxy 21 is needed. Another method is to press the pad onto the conductive pattern and hold it in place with a non-conductive epoxy. Yet another alternative technique is to ultrasonically bond the die pads to the conductive pattern. From the various evolving techniques, slight cost advantages have been recognized through different implementations. However, the methods generally suffer from slow throughput and high cost since each die must be placed and attached individually which most often requires physical handing by a technician.
It should also be recognized that low frequency (<100 MHz) tags do not require a space between the conductive pattern and the die. This is not the case with high frequency (>400 MHz) tags where a space must be maintained in order to assure that the coupling between the two elements does not cause a detuning of the final assembled tag. Therefore, new methods must be able to efficiently attach low and high frequency tags.
In light of this problem, it is an object of the present invention to provide a die attachment design that allows for mechanical alignment and direct attachment of die to a conductive module, thereby eliminating the intermediate step of physically handling the die. It is yet another object of the present invention to provide a design that enables multiple die to be attached near simultaneously by aligning the multiple die to multiple conductive modules. Yet another object of the present invention is to provide a die attachment method that employs the use of laser light or ultrasonic bonding to make electrical connections between the die and the conductive module. Yet still another object of the present invention is to provide a die attachment method that employs the use a photosensitive hardening material to structurally secure the die to the conductive module. Finally, it is further an object of the invention to provide a design and method that reduces the cost die attachment.